<template>
    <div class="article-list" ref="article-list">
        <van-pull-refresh
        v-model="isRefreshLoading"
        :success-text="refreshSuccessText"
        :success-duration="1500"
        @refresh="onRefresh"
        >
        <van-list
          v-model="loading"
          :finished="finished"
          finished-text="没有更多了"
          @load="onLoad"
        >
        <article-item
        v-for="(article,index) in articles"
        :key="index"
        :article="article"
        />
          <!-- <van-cell
            v-for="(article,index) in articles"
            :key="index"
            :title="article.title"
          /> -->
        </van-list>
        </van-pull-refresh>
    </div>
</template>

<script>
import { getArticles } from '@/api/article'
import ArticleItem from '@/components/article-item'
import { debounce } from 'lodash'

export default {
    name: 'ArticleList',
    components: {
        ArticleItem
    },
    props: {
        channel: {
            type: Object,
            required: true
        }
    },
    data () {
        return {
            articles: [], //数据列表
            loading: false, //控制加载中的 loading 状态
            finished: false, //控制加载结束的状态，当加载结束，不再触发加载更多
            timestamp: null, //获取下一页数据的时间戳
            isRefreshLoading: false, //下拉刷新的 loading 状态
            refreshSuccessText: '', //下拉刷新成功的提示文本
            scrollTop: 0 // 列表滚动到顶部的距离
        }
    },
    computed: {},
    watch: {},
    created () {},
    mounted () {
        const articleList = this.$refs['article-list']
        articleList.onscroll = debounce(() => {
            this.scrollTop = articleList.scrollTop
        }, 50)
    },
    // 把记录的到顶部的距离重新设置回去
    activated () {
        this.$refs['article-list'].scrollTop = this.scrollTop
    },
    methods: {
       async onLoad () {
      // 1.请求获取数据
      const { data } = await getArticles({
          channel_id: this.channel.id, //频道 ID
          timestamp: this.timestamp || Date.now()
      })

      // 2.把数据放到 list 数组中
      const { results } = data.data
      this.articles.push(...results)
      // 3.设置本次加载状态结束，它才可以判断是否需要加载下一次，否则就会永远的停在这里
      this.loading = false
      // 4.数据全部加载完成
      if(results.length) {
          //更新获取下一页数据的页码
          this.timestamp = data.data.pre_timestamp
      } else {
          //没有数据了，把加载状态设置结束，不再触发加载更多
          this.finished = true
      }
    },

    async onRefresh () {
        // 下拉刷新，组件自己就会展示 loading 状态
        // 1. 请求获取数据
        const { data } = await getArticles({
          channel_id: this.channel.id, //频道 ID
          timestamp: Date.now()
      })

        // 2. 把数据放到数据列表中 (往顶部追加)
        const { results } = data.data
        this.articles.unshift(...results)

        // 3. 关闭刷新的状态
        this.isRefreshLoading = false

        this.refreshSuccessText = `更新了${results.length}条数据`
    }
    }
}
</script>

<style scoped>
.article-list{
    position: fixed;
    left: 0;
    right: 0;
    bottom: 50px;
    top: 90px;
    overflow-y: auto;
}
</style>